The present invention generally relates to a method and system for heating semiconductor wafers coated with reflective surfaces. More particularly, the present invention is directed to a method and system for uniformly heating a wafer coated with a reflective coating by placing a ceramic shield adjacent to the wafer.
A thermal processing chamber as used herein refers to a device that rapidly heats objects, such as semiconductor wafers. Such devices typically include a substrate holder for holding a semiconductor wafer and a light source that emits light energy for heating the wafer. During heat treatment, the semiconductor wafers are heated under controlled conditions according to a preset temperature regime. During heating, various processes can be carried out within the thermal processing chamber, such as rapid thermal oxidation, reduction, nitridation, annealing, and silicidation.
Many semiconductor heating processes require a wafer to be heated to high temperatures so that the various chemical and physical transformations can take place as the wafer is fabricated into a device. During rapid thermal processing, for instance, semiconductor wafers are typically heated by an array of lights to temperatures from 400xc2x0 C. to about 1200xc2x0 C., for times that are typically less than a few minutes. During these processes, the main goal is to heat the wafers as uniformly as possible.
In the past, in order to control the temperature of a wafer during heating and in order to heat the wafer as uniformly as possible, the temperature of the wafer was monitored during heating and this information was sent to a controller for controlling the heating source in the thermal processing chamber in a manner that heated the wafer as desired. In order to monitor the temperature of the wafer during heating, one or more pyrometers were used. A pyrometer measures the temperature of the wafer by sensing the amount of thermal radiation being emitted by the wafer. Of particular advantage, pyrometers can measure the temperature of the wafers without contacting the wafers.
However, in some applications, conventional methods of heating semiconductor wafers are not effective. For example, semiconductor wafers are often coated with a reflective-material such as copper. Typically, a reflective surface will reflect much of the heat emitted by a thermal processing chamber. As a result, the intensity of the heat source must be significantly increased so that the semiconductor wafer can absorb the energy required to increase in temperature to a desired level. Furthermore, the reflective surface can make it much more difficult to accurately monitor and control the temperature of the wafer.
As such, a need currently exists for a system and method of uniformly heating a semiconductor wafer having a reflective surface. A need also exists for a system that monitors and controls the temperature of a semiconductor wafer coated with a reflective surface.
The present invention recognizes and addresses the foregoing disadvantages, and others of prior art constructions and methods.
Accordingly, it is an object of the present invention to provide an improved method and system for heating semiconductor wafers coated with reflective materials.
Another object of the present invention is to provide a method and system for uniformly heating a semiconductor wafer coated with a reflective material.
Still another object of the present invention is to provide a system and method for monitoring and controlling the temperature of a semiconductor wafer coated with a reflective material during thermal processing.
It is another object of the present invention is to provide a method and system for effectively heating semiconductors wafers having a reflective surface using a ceramic shield member positioned adjacent to the wafer.
These and other objects of the present invention are achieved by providing an apparatus for heating semiconductor wafers that are coated with a reflective surface, such as copper. The apparatus includes a thermal processing chamber adapted to contain and heat semiconductor wafers. In particular, for heating the wafers, a heating device is placed in communication with the thermal processing chamber. The heating device can include, for instance, a plurality of light energy sources that emit thermal light energy onto the wafers.
In accordance with the present invention, a shield member is contained within the thermal processing chamber and is positioned adjacent to the semiconductor wafer coated with a reflective surface being heated. The shield member is placed in direct association with the heating device. The shield member is made from a material that increases in temperature when contacted with light energy. For instance, the shield member can be made from a ceramic material.
In one embodiment, the shield member is generally placed within about 10 millimeters above the semiconductor wafer, and particularly between about 3 millimeters to about 8 millimeters above the wafer. Due to its close proximity to the wafer, the shield member can absorb much of the light energy being emitted by the heating device and reflected by the reflective surface of the semiconductor wafer. By absorbing light energy, the shield member increases in temperature and then transfers heat to the wafer until the wafer is heated to an appropriate temperature. As a result, the semiconductor wafer can be heated at a faster rate than otherwise would be possible.
The present invention is particularly well suited for heating copper-coated semiconductor wafers in the presence of ambient gases during thermal processing. For example, a copper-coated semiconductor wafer can be heated in the presence of oxidizing and reducing gases for circuit fabrication.
In one embodiment of the present invention, a copper-coated semiconductor wafer can first be heated in accordance with the present invention in the presence of oxidizing gases, such as oxygen, water vapor, or other oxidizing gases in order to form an oxide coating on the wafer. In general, the wafer can be heated to a temperature between about 100xc2x0 C. to about 600xc2x0 C., and particularly between about 200xc2x0 C. to about 450xc2x0 C. Thereafter, the copper oxide-coated semiconductor wafer is then heated in the presence of a reducing ambient gas, such as hydrogen according to the present invention. The reducing atmosphere converts the copper oxide coating back into copper. During this transformation, copper reflow occurs creating a smooth and uniform copper surface.
A temperature sensing device can be placed in association with the shield member for monitoring the temperature of the shield member during thermal processing. According to the present invention, by monitoring the temperature of the shield member during thermal processing, the temperature of the semiconductor wafer coated with the reflective material can be derived. In particular, a calibration can be constructed for determining a relationship between the temperature of the shield member and the temperature of the semiconductor wafer.
For instance, in one embodiment, the temperature of the shield member can be monitored using one or more thermocouples. In this manner, thermocouples can be used to monitor the temperature of the semiconductor wafer coated with the reflective material without having to actually contact the wafer. It should be understood however, that besides thermocouples, other temperature sensing devices can be used to monitor the shield member temperature. For example, pyrometers can also be used to monitor the temperature.
The system of the present invention can also include a controller, such as a microprocessor, which can be placed in communication with the temperature sensing devices and the heating device. Based upon the temperature received from the temperature sensing devices, the controller can be programmed to control the amount of thermal energy being emitted by the heating device for heating the wafer according to a preset temperature regime.
Other objects, features and aspects of the present invention are discussed in greater detail below.